In recent years, there is a worldwide increasing interest in the protection of the ozone layer and the problem of earth warming, and an improvement of refrigerants used in the refrigerating cycle of a refrigerator, an air conditioner and so on has be required. At present, most of refrigerators on sale use HFC (hydrofluorocarbon) as a refrigerant. However, the HFC cooling medium still has a high earth warming coefficient. Therefore, the use of a hydrocarbon cooling medium which is free of the destruction of the ozone layer and has a low earth warming coefficient, for example, an HC (hydrocarbon) cooling medium has been studied.
The HC cooling medium is a combustible cooling medium, so that a risk of ignition is pointed out. However, as the flow per volume thereof is larger than that of the HFC cooling medium, the necessary amount of the refrigerant charged into the refrigerating cycle may be smaller than a half of that of the HFC cooling medium. Therefore, even if the refrigerant leaks from the refrigerating cycle, there is little possibility of increasing to the ignition concentration, and in a refrigerator provided with the explosion-proof treated electrical parts, the safety thereof is high.
However, the HC cooling medium has is characteristically easily soluble into the refrigeration machine oil, for example, a mineral oil, in contrast to the solubility of an HFC cooling medium and other refrigerants in the machine oil. Therefore, a problem arises that the amount of the refrigerant circulating in the refrigerating cycle decreases. In particular, after turning on power when much refrigerant has been dissolved in the refrigeration machine oil, there is the possibility that cooling performance will be reduced.
It is generally known that at a low temperature and a high pressure, the amount of the HC cooling medium dissolved into the refrigeration machine oil increases. Therefore, when a refrigerator is installed in winter, the compressor and so on are in a low temperature state, so that even if power is turned on after the installation, the amount of refrigerant dissolved in the refrigeration machine oil is large. Moreover the temperature of the compressor cannot easily rise because the atmospheric temperature is low. Thus as the dissolved refrigerant will not be separated from the refrigeration machine oil, and particularly after power is turned on, the amount of the refrigerant circulating in the refrigerating cycle reduces, and the start-up of the initial cooling performance is extremely bad.
Furthermore, since the charged amount of HC cooling medium is small, the effect due to the dissolving into the refrigeration machine oil is high and the cooling performance is reduced. The reason is that even if the dissolved amount of HC cooling medium is the same as that of the HFC cooling medium, the charged amount of the HC cooling medium is smaller than a half of that of the HFC cooling medium, so that the reduction rate of the amount of the circulating refrigerant due to the dissolution is doubled or more, and the cooling performance is reduced according to the reduction rate.
On the other hand, an HC cooling medium has a high solubility into refrigeration machine oil at high pressure. As the pressure in the compressor is higher than that during the normal running until the pressure of the refrigerating cycle is made uniform and the pressure in the compressor is reduced after turning on power, so that the amount dissolved in the refrigeration machine oil is large and the cooling performance in this period is particularly low.
Next, conventionally, to perform cooling running of the refrigerator, a cooling fan is rotated in synchronization with the driving of the compressor for circulating the refrigerant in the refrigerating cycle so as to radiate heat from the compressor and the condenser. The reason is that the temperatures of the compressor and condenser are lowered, thus the condensation temperature of the refrigerant is lowered, and the cooling capacity is improved, and the loss due to rise of the winding temperature of a compressor motor is reduced.
On the other hand, when the air temperature is low, for example, when the temperature of the installation location of the refrigerator is 10° C. or lower, the temperature of the compressor may be excessively lowered due to the driving of the cooling fan. When the temperature of the compressor is lowered lower than required, the amount of the refrigerant dissolved in the refrigeration machine oil is increased and a so-called refrigerant sleeping phenomenon that the refrigerant does not circulate in the refrigerating cycle and the cooling performance is lowered is generated (the amount of circulating refrigerant is reduced).
As a sleeping countermeasure, an air temperature sensor for detecting the room temperature is installed respectively on the hinge portion and the operation board and when the air temperature detected by the sensors is low, the cooling fan is stopped independently of driving of the compressor, thus the compressor and the condenser are prevented from overcooling and the sleeping of refrigerant is suppressed.
However, even when the air temperature is a medium temperature that is higher than the low temperature, for example, 10° C. to 20° C., depending on the conditions of the installation location, the refrigerant sleeping phenomenon is generated, causing defective cooling.
For example, when a refrigerator is to be installed in a place at a low air temperature in winter, the refrigerator is stored before installation in a place at a low air temperature such as a warehouse, and fixed to the bed of a truck during delivery, so that the refrigerator is kept in a low temperature state. However, the installation location is heated by a heating system and is warm, so that the air temperature sensors of the installed refrigerator detect medium temperature or high temperature.
Therefore, even when the temperature around the installation location is higher than a predetermined temperature, the refrigerator body, in particular the compressor having high heat capacity is kept in a low temperature state, so that the refrigerant dissolved in the refrigeration machine oil is not circulated in the refrigerating cycle. Moreover, as the air temperature sensors detect medium temperature or high temperature, the cooling fan rotates and more excessively cools the compressor and the condenser, causing sleeping of the refrigerant.
Further, even when the room at the installation location is heated by a heating apparatus and is warm, as the warm air go up and by a draft from the door, the ambient temperature of the floor is mostly lower than the room temperature. Generally, the air temperature sensors are arranged on the upper part of the refrigerator body such as the hinge portion and the operation board, so that even if the sensors detect medium temperature or high temperature as a room temperature, the machine room may be in a low temperature state because it is positioned around the floor.
Therefore, although the compressor and the condenser are in the low temperature state, the air temperature sensors detect medium temperature or high temperature. Accordingly, the cooling fan rotates and excessively cools the compressor and the condenser, causing sleeping of the refrigerant.
On the other hand, in recent years, there is a worldwide increasing interest in the protection of the ozone layer and the problem of the earth warming. The use of a combustible cooling medium, for example, an HC (hydrocarbon) cooling medium has be studied which is free of destruction of the ozone layer and has a low earth warming coefficient compared with the conventional refrigerants, for example, R134a. For the HC refrigerant, in consideration of the cooling capacity thereof and the safety at the time of leakage, the charged amount of the refrigerant can be reduced to less than a half of that of R134a.
However, when the HC refrigerant which is to be charged in a small amount is used, if the same sleeping amount as that of R134a is generated, the ratio of the amount of the sleeping refrigerant to the total amount of the refrigerant is more than two times of the conventional ratio. Thus, even for a small amount of the sleeping refrigerant, the reduction ratio of the circulating amount of the refrigerant is enlarged, so that the cooling performance is extremely lowered.
The present invention was developed with the foregoing problems in view, and is intended to provide a refrigerator which has initial high cooling performance after turning on power even if a hydrocarbon cooling medium a small amount of which is charged and which is easily soluble in a refrigeration machine oil is used.
Also, the present invention was developed with the foregoing problems in view, and is intended to provide a refrigerator for preventing the defective cooling due to the sleeping of a refrigerant staying in a compressor and a condenser.